Recovery of phosphorus values and salt impurities from aqueous waste streams

ABSTRACT

The present invention generally relates to processes for recovery of phosphorus values and salt impurities from aqueous waste streams. In particular, the present invention relates to processes for recovery of phosphorus values and salt impurities from aqueous waste streams generated in the manufacture of phospho-herbicides, including N-(phosphonomethyl)glycine and glufosinate.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/319,811, filed Dec. 22, 2011, which issued Mar. 11, 2014 as U.S. Pat.No. 8,669,396, and which is the U.S. National Stage of International PCTApplication No. PCT/US2010/034696, filed May 13, 2010, and claims thebenefit of U.S. Provisional Patent Application Ser. No. 61/179,158,filed May 18, 2009, the entire disclosures of which are incorporatedherein by reference.

FIELD OF THE INVENTION

The present invention generally relates to processes for recovery ofphosphorus values and salt impurities from aqueous waste streams. Inparticular, the present invention relates to processes for recovery ofphosphorus values and salt impurities from aqueous waste streamsgenerated in the manufacture of phospho-herbicides, includingN-(phosphonomethyl)glycine and glufosinate.

BACKGROUND OF THE INVENTION

N-(phosphonomethyl)glycine (glyphosate) and its salts are convenientlyapplied as a component in aqueous, post-emergent herbicide formulations.As such, they are particularly useful as highly effective andcommercially important broad-spectrum herbicides for killing orcontrolling the growth of a wide variety of plants, includinggerminating seeds, emerging seedlings, maturing and established woodyand herbaceous vegetation and aquatic plants.

Various methods for preparation of glyphosate have been developed. Onemethod includes the catalyzed liquid phase oxidative cleavage of acarboxymethyl substituent from an N-(phosphonomethyl)iminodiacetic acid(PMIDA) substrate. Over the years, a wide variety of methods and reactorsystems have been disclosed for conducting this oxidation reaction. Seegenerally, Franz, et al., Glyphosate: A Unique Global Herbicide (ACSMonograph 189, 1997) at pp. 233-62 (and references cited therein);Franz, U.S. Pat. No. 3,950,402; Hershman, U.S. Pat. No. 3,969,398;Felthouse, U.S. Pat. No. 4,582,650; Chou, U.S. Pat. No. 4,624,937; Chou,U.S. Pat. No. 4,696,772; Ramon et al., U.S. Pat. No. 5,179,228;Siebenhaar et al., International Publication No. WO 00/01707; Ebner etal., U.S. Pat. No. 6,417,133; Leiber et al., U.S. Pat. No. 6,586,621;and Haupfear et al., U.S. Pat. No. 7,015,351.

The reaction may be conducted in either a batch or continuous oxidationreactor system in the presence of a catalyst that typically comprisesparticulate carbon, or a noble metal such as platinum on a particulatecarbon support. The catalyst is usually slurried in an aqueous solutionof PMIDA within a stirred tank reactor, and molecular oxygen isintroduced into the reactor to serve as the oxidizing agent. Thereaction is exothermic. The liquid phase oxidation of a PMIDA substratetypically produces a reaction mixture containing water and variousimpurities besides the desired N-(phosphonomethyl)glycine product. Theseimpurities may include, for example, various by-products, unreactedstarting materials, as well as impurities present in the startingmaterials. Representative examples of impurities present inN-(phosphonomethyl)glycine product reaction mixtures include, forexample, unreacted PMIDA substrate, N-formyl-N-(phosphonomethyl)glycine(NFG), phosphoric acid, phosphorous acid,N-methyl-N-(phosphonomethyl)glycine (NMG), glycine,aminomethylphosphonic acid (AMPA), methyl aminomethylphosphonic acid(MAMPA), iminodiacetic acid (IDA), imino-bis-(methylene)-bis-phosphonicacid (iminobis), formaldehyde, formic acid, chlorides, and ammoniumsulfate.

Other methods for preparation of glyphosate utilize different startingmaterials including, for example, glycine, which is used in theso-called “alkylphosphite process.” See, for example, Chinese PatentDisclosure No. CN 1629112A. Such methods are often referred to elsewhereand herein as the “glycine method” or “glycine route.” These methodsgenerally comprise dissolving formaldehyde or paraformaldehyde in asolvent (typically methanol (MeOH)) containing triethylamine followed byaddition of glycine. After addition and dissolution of glycine,dimethylphosphite is added, followed by addition of hydrochloric acid(HCl) to produce a mixture of HCl, glyphosate, and methyl chloride.Neutralization by addition of a base provides the glyphosate salt(s).Alternatively, trimethylphosphite may be used as the starting material.Methyl chloride may be recovered and utilized in the manufacture oforganosilane products as described, for example, in Chinese PatentDisclosure No. CN 1446782. As with the PMIDA-based method describedabove, preparation of glyphosate in this manner results in a reactionmixture containing a variety of impurities including, for example,glycine, N,N-bis(phosphonomethyl)glycine (glyphosine), phosphorous acid,phosphoric acid, hydroxymethylphosphonic acid, and triethylaminehydrochloride (Et₃N.HCl). Recovery of triethylamine (e.g., using astrong base such as sodium hydroxide (NaOH)) can improve the processeconomics.

Glyphosate may be produced from glycine, e.g., by a process as describedin U.S. Pat. No. 4,486,359, which is expressly incorporated in itsentirety herein by reference for all relevant purposes. In this process,glycine is initially reacted with paraformaldehyde in the presence oftriethylamine to produce N,N-bis(hydroxymethyl)glycine. The reaction isconducted in a methanol medium, typically at MeOH reflux temperature(i.e., about 65° C.). The N,N-bis(hydroxymethyl)glycine intermediate isreacted with dimethyl phosphite to yield an ester, which U.S. Pat. No.4,486,359 characterizes as the methyl ester of glyphosate. The ester ishydrolyzed in HCl to glyphosate acid. This product generally has aglyphosine content in excess of 0.010 wt. %, more typically betweenabout 0.05% and about 2% on a glyphosate, a.e., basis. Commercialsources of glycine process glyphosate may commonly contain between about0.2% and about 1.5% by weight glyphosine and between about 0.05% andabout 0.5% by weight glycine, more typically between about 0.3 and about1% by weight glyphosine and between about 0.1 and about 0.3% by weightglycine, all on a glyphosate, a.e., basis.

In an alternative to the process of U.S. Pat. No. 4,486,359, JapanesePublished Application Hei 9-227583 (application no. Hei-9-6881)describes a process in which the reaction between paraformaldehyde andglycine may be conducted in the presence of tributylamine rather thantriethylamine, and the ester intermediate may be hydrolyzed in analkaline medium such as NaOH rather than in acidic medium such as HCl.The Japanese patent publication reports that the base hydrolysis mayproduce a product of lower glyphosine content than the product of theprocess of U.S. Pat. No. 4,486,359.

In conducting the process of Japanese Published Application Hei9-227583, a source of formaldehyde, preferably paraformaldehyde is mixedwith a reaction medium comprising C₁ to C₄ alcohol at moderatelyelevated temperature, tributylamine is added to the resulting solutionand the mixture preferably agitated at about 35° C. to 50° C. fortypically 30 to 60 minutes. Glycine is added to the alcohol medium in aproportion which preferably assures a formaldehyde to glycine molarratio from about 1 to 5, and the glycine is preferably completelydissolved in the medium. Preferably, the molar ratio of tributylamine toglycine is from about 0.5 to about 3. The temperature is maintained atleast about 30° C., preferably between about 50° C. and about 60° C. fortypically about 10 to 60 minutes, resulting in reaction of glycine withformaldehyde to form the tributylamine salt of N-methylolglycine. Adialkylphosphite, e.g., dimethylphosphite, is then added to the solutionunder agitation at elevated temperature, preferably at least about 50°C., more typically about 65° C. to about 80° C., conveniently underalcohol reflux, preferably at a molar ratio to N-methylolglycine fromabout 0.6 to about 2.0. The dialkylphosphite condenses with thetributylamine salt of N-methylolglycine to yield an ester intermediatedepicted in the Japanese patent publication as the dialkyl ester of thetributylamine carboxylate salt of glyphosate. Addition of a strong basesuch as NaOH to this solution saponifies the ester, liberatestributylamine and forms the sodium salt of glyphosate. The reactionmixture separates into two liquid phases, yielding an upper layercontaining tributylamine and a lower layer comprising a solution ofsodium salt of glyphosate. Tributylamine may be recovered from the upperlayer for recycle. The lower layer may be acidified to crystallizeglyphosate acid.

The alkaline hydrolysis may be conducted with a strong base comprising adesired countercation such as, e.g., potassium hydroxide (KOH), as astep in the preparation of an aqueous concentrate of the potassium saltof glyphosate. Where the phase separation is carried out underconditions that assure substantially quantitative partition oftributylamine to the upper layer, the lower layer may be used directlyin the preparation of an aqueous glyphosate concentrate comprising thepotassium salt. Alternatively, the glyphosate salt may be acidified toprecipitate glyphosate acid, and the glyphosate acid separated byfiltration or centrifugation and washed, and the washed glyphosate wetcake reslurried with water and base to produce the desired salt. In thelatter process, the advantage of using KOH for the conversion ofintermediate ester to glyphosate salt is diminished. Where triethylamineis used as the alkylamine, it can be quantitatively removed bydistillation of the hydrolyzate, which may in certain instancesfacilitate direct preparation of a concentrate of the glyphosate salt ofthe base used for the conversion of the intermediate ester. Preferably,the concentrate comprises at least about 360 grams per liter (g/L)glyphosate on an acid equivalent (a.e.) basis.

Regardless of the precise method by which a glyphosate product ismanufactured, a concentrated glyphosate product, or wet cake can beprepared from the resulting reaction product solution. Preparation ofthe glyphosate wet cake also produces a filtrate, or mother liquor thatcontains various impurities, along with a portion of the glyphosateproduct not isolated in the wet cake. The glyphosate present in thefiltrate, or mother liquor may represent up to 10% (e.g., from 5% to10%) of the glyphosate produced.

In addition to the above-noted processes (e.g. PMIDA-based and glycineroutes), glyphosate product may be manufactured by processes that useAMPA as the substrate. Both glycine and AMPA-based processes generate aprofile of by-products and impurities that is somewhat different fromthat of the PMIDA oxidation process. For example, the product of theglycine process most typically contains glyphosine in a concentrationgreater than about 0.010 wt. %, more typically at least about 0.1 wt. %,and most typically in the range of about 0.3 to about 1 wt. %, all on aglyphosate a.e. basis. The product of the AMPA-based process may have amodest to significant fraction of unreacted AMPA, though the product ofthe PMIDA process can have a comparable AMPA content. The glycinecontent of the AMPA process product is generally significantly lowerthan 0.02 wt. % on a glyphosate, a.e., basis.

To capitalize on the glyphosate present in the mother liquor, glyphosateproducts have been prepared by adding relatively pure glyphosate to themother liquor to produce a solution of glyphosate containing, forexample, approximately 10 wt. % of glyphosate. Unfortunately, however,glyphosate product solutions prepared in this manner typically contain acomparable level of salt (e.g., sodium chloride) along with otherimpurities associated with the manufacture of glyphosate. Utilizing aglyphosate product containing such high levels of sodium chloride inagricultural applications is undesired for environmental reasons.

Recovery of valuable products from the filtrate, or mother liquor,produced during glyphosate manufacture would improve the overalleconomics of glyphosate manufacturing processes while avoiding theundesired environmental consequences associated with current practices.More particularly, providing effective recovery of phosphorus and saltvalues from the filtrate would substantially reduce, and preferablyeliminate completely the desirability of preparing glyphosate productsof high impurity (e.g., sodium chloride) content directly from themother liquor.

In addition, commercial processes for manufacture of glyphosate mayinclude deepwell injection of various waste streams, including themother liquor resulting from wet cake production. Deepwell injection hasbeen and may be practiced in an environmentally responsible manner.However, a method for treatment of waste streams that provides recoveryof valuable products as an alternative to deepwell injection would bedesirable in the event that deepwell injection of waste streams fromglyphosate manufacture is not permitted or commercially practical.

Accordingly, there exists an unfulfilled need in the art for processesfor recovery of values from the mother liquor generated in production ofglyphosate wet cake and other aqueous waste streams generated in themanufacture of glyphosate, as well as from aqueous process streamsgenerated in the manufacture of glyphosate precursors (e.g. PMIDA).

SUMMARY OF THE INVENTION

Briefly, therefore, the present invention is directed to processes forthe recovery of phosphorus values and salt impurities from aqueous wastestreams comprising organic phosphorus compounds and salt impurities. Inone embodiment, the process comprises oxidizing one or more compoundscontaining phosphorus and organic carbon present in a feed streamcomprising components of the aqueous waste stream to produce aphosphate-containing cake; contacting within an acidification zone thephosphate-containing cake and an acidic liquid medium to form a solutioncomprising at least one inorganic salt and phosphoric acid; andprecipitating salt crystals from the salt-containing solution to form anaqueous product mixture comprising salt crystals and a mother liquorcomprising phosphoric acid.

In another embodiment, the process comprises passing a feed streamcomprising components of the aqueous waste stream through an atomizingnozzle to form an atomized aqueous waste stream; introducing theatomized aqueous waste stream into a combustion chamber; and combustingone or more compounds containing phosphorus and organic carbon containedin the atomized aqueous waste stream with an oxygen-containing gas at atemperature of from about 600° C. to about 800° C. to form a combustiongas stream comprising carbon dioxide, phosphorus oxide and particulatesalt impurities. The process further comprises separating theparticulate salt impurities from the combustion gas stream; andcontacting the combustion gas stream with an aqueous scrubbing liquid toproduce phosphoric acid.

In a further embodiment, the process comprises oxidizing one or morecompounds containing phosphorus and organic carbon present in a feedstream comprising components of the aqueous waste stream to produce aphosphate-containing stream and a solid containing inorganic salts; andcontacting the phosphate-containing stream with an acidic liquid mediumto form phosphoric acid.

The present invention is also directed to processes for recovery of anN-(phosphonomethyl)glycine product from an aqueous process streamfurther comprising one or more impurities. In one embodiment, theprocess comprises contacting the aqueous process stream with a selectivemembrane to produce a retentate comprising N-(phosphonomethyl)glycineand a permeate comprising N-(phosphonomethyl)glycine and one or moreimpurities. The retentate is enriched in N-(phosphonomethyl)glycinerelative to the permeate. The process further comprises introducing thepermeate into an ion exchange zone and contacting the permeate with atleast one ion exchange resin contained therein for selective removal ofN-(phosphonomethyl)glycine therefrom to form an ion exchange zoneeffluent comprising impurities and depleted inN-(phosphonomethyl)glycine relative to the permeate.

The present invention is also directed to processes for recovery of saltimpurities from an aqueous waste stream. In one embodiment the processcomprises subjecting the aqueous waste stream to a temperature above thesupercritical temperature of the aqueous waste stream and a pressureabove the supercritical pressure of the aqueous waste stream.

Other objects and features will be in part apparent and in part pointedout hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flowsheet depicting one embodiment of a process for recoveryof phosphorus values and salt impurities from an aqueous waste streamgenerated in glyphosate manufacture.

FIG. 2 is a flowsheet depicting another embodiment of a process forrecovery of phosphorus values and salt impurities from an aqueous wastestream generated in glyphosate manufacture.

FIG. 3 is a flowsheet depicting one embodiment of a process for recoveryof glyphosate from an aqueous waste stream.

FIG. 4 is a flowsheet depicting another embodiment of a process forrecovery of glyphosate from an aqueous waste stream.

FIG. 5 is a flowsheet depicting a further embodiment of a process forrecovery of glyphosate from an aqueous waste stream.

FIG. 6 is a flowsheet depicting a laboratory evaluation system utilizedas set forth in Examples 4-6.

Corresponding reference characters indicate corresponding partsthroughout the drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Described herein are processes for recovery of phosphorus values andsalt impurities from aqueous waste streams comprising phosphoruscompounds (e.g., inorganic and organic phosphorus compounds) and one ormore salt impurities. Processes of the present invention are suitablefor recovery of phosphorus values and salt impurities from a variety ofaqueous waste streams, including aqueous waste streams generated in themanufacture of phospho-herbicides. For example, described herein areprocesses for recovery of phosphorus values and salt impurities fromaqueous waste streams generated in the manufacture of glyphosate andglufosinate. Similarly, the processes of the present invention are alsosuitable for recovery of phosphorus values and salt impurities fromaqueous process streams generated in the manufacture of precursors ofphospho-herbicides such as glyphosate. For example, various embodimentsof the present invention are directed to recovery of phosphorus valuesand salt impurities from aqueous waste streams comprising the glyphosateprecursor PMIDA.

Much of the following discussion focuses on processes for recovery ofphosphorus values and salt impurities from aqueous waste streamsgenerated in the manufacture of glyphosate, but it is to be understoodthat the processes detailed herein may be readily adapted to recovery ofphosphorus values and salt impurities from various other waste streamscomprising various organic phosphorus compounds and salt impurities.

In commercial practice, the PMIDA-based route of glyphosate manufacturetypically produces aqueous waste streams (e.g., mother liquor generatedin glyphosate wet cake production) containing up to approximately 2 wt.% glyphosate, up to approximately 10 wt. % sodium chloride, variousphosphonic acids, ammonium sulfate, and various other impurities.Similarly, the glycine route for glyphosate manufacture produces aqueouswaste streams of similar glyphosate and sodium chloride content, alongwith glyphosine, glycine, phosphorous acid, phosphoric acid,hydroxymethylphosphonic acid, and various other impurities.

Recovery of inorganic salts (e.g., sodium chloride) and phosphorusvalues (e.g., phosphoric acid) from these waste streams provides valuein view of the recovery of these products. In addition, these recoveryprocesses represent an economically viable alternative to utilizing thewaste streams to prepare glyphosate products having high impuritycontent. These recovery processes also provide alternatives to dischargeof these waste streams into surface waters or deepwells.

Also described herein are processes for recovery of glyphosate fromaqueous waste streams generated in the manufacture thereof. As noted,glyphosate present in these waste streams may represent up toapproximately 5 to 10% by weight of the total glyphosate produced.Accordingly, in addition to recovery of phosphorus and salt values,recovery of glyphosate from the waste stream improves the overalleconomics of the process. Recovery of glyphosate may be carried oututilizing a variety of methods including, for example, evaporativecrystallization, membrane separation and ion exchange techniques.Similarly, also described herein are processes for recovery of one ormore glyphosate precursors (e.g., PMIDA), along with recovery ofphosphorus values and salt impurities. Glyphosate precursors such asPMIDA and precursors of PMIDA recovered in accordance with the processesof the present invention may be utilized in preparation of glyphosate.

It is to be understood that reference to “phosphorus values” refers tophosphorus recovered from the waste stream, regardless of the source ofthe phosphorus. For example, recovered phosphorus values may be derivedfrom organic phosphorus compounds (e.g., glyphosate, PMIDA,aminomethylphosphonic acid, hydroxymethylphosphonic acid,N-formyl-N-(phosphonomethyl)glycine,N-methyl-N-(phosphonomethyl)glycine, methyl aminomethylphosphonic acidand salts thereof), and may also be provided by other components of theaqueous waste stream (e.g., phosphoric acid, phosphorous acid, and saltsthereof). Typically, as detailed elsewhere herein, phosphorus values arerecovered in the form of phosphoric acid.

A. Recovery of Phosphoric Acid and Sodium Chloride

Various embodiments of the processes of the present invention compriseoxidizing one or more compounds containing phosphorus and organic carbonpresent in a feed stream comprising components of the aqueous wastestream. As detailed elsewhere herein, oxidation of these components ofthe waste stream may be conducted by calcination of the aqueous wastestream and/or combustion of components of the aqueous waste stream.

The organic carbon and phosphorus to be oxidized may be present in oneor more components of the aqueous feed stream. For example, in the caseof an aqueous waste stream generated in the PMIDA-based route ofglyphosate manufacture, organic carbon may be present in glyphosate,PMIDA, and various by-products of PMIDA oxidation, including formicacid, formaldehyde, and various other impurities. Phosphorus to beoxidized in such waste streams is typically present in glyphosate,unreacted PMIDA substrate, N-formyl-N-(phosphonomethyl)glycine, NMG,phosphoric acid, phosphorous acid, AMPA, and MAMPA. In the case ofaqueous waste streams generated in the glycine-based route of glyphosatemanufacture, organic carbon may be present in glycine, glyphosate,glyphosine, NMG, hydroxymethylphosphonic acid, AMPA, and MAMPA.Phosphorus to be oxidized in glycine-based route waste streams may bepresent in glyphosate, glyphosine, phosphorous acid, phosphoric acid,and hydroxymethylphosphonic acid.

Generally, oxidizing compounds containing phosphorus and organic carbonproduces a phosphate-containing cake that is contacted with an acidicliquid medium to form a solution comprising at least one inorganic salt(e.g., sodium chloride) and phosphoric acid. Salt crystals are typicallyprecipitated from the salt-containing solution to form an aqueousproduct mixture comprising salt crystals and a mother liquor comprisingphosphoric acid.

Further in accordance with the present invention, the process typicallycomprises separating salt crystals and the phosphoric acid-containingmother liquor. The salt crystal fraction may be washed to produce apurified salt product exhibiting one or more desired properties (e.g.,total organic carbon (TOC) content, total nitrogen content, and/or totalphosphate content, as specified elsewhere herein). Additionally oralternatively, the salt product is typically dissolved in an aqueousmedium to form a brine solution. Also in accordance with the presentinvention, and as detailed elsewhere herein, phosphoric acid istypically extracted from the mother liquor fraction by suitable methods,including liquid-liquid extraction.

FIG. 1 depicts one embodiment of a process for recovering phosphorusvalues and salt impurities from an aqueous waste stream generated in themanufacture of glyphosate. It is to be understood that the processdepicted in FIG. 1 is not limited to recovery of phosphorus values andsalt impurities from aqueous waste streams generated in the manufactureof glyphosate, and is generally suitable for recovery of phosphorusvalues and salt impurities from a variety of aqueous waste streamsemanating from the manufacture of phospho-herbicides.

As shown, feed stream 1 comprising components of the aqueous wastestream is introduced into a concentration vessel, or evaporator 5 toremove water and one or more other impurities in overheads stream 9.Various conventional methods for the manufacture of glyphosate generateaqueous waste streams comprising organic impurities includingformaldehyde and formic acid. As shown in FIG. 1, concentration of feedstream 1 removes water, formaldehyde, and formic acid in overheadsstream 9.

It is to be understood that removal of water and one or more organicimpurities from feed stream 1 is not limited to evaporation orconcentration and may suitably be conducted by various other means. Forexample, in various embodiments, water and one or more organicimpurities are removed from the waste stream by contacting the wastestream with a separation membrane to form a retentate comprising organicphosphorus compounds and a permeate comprising water and one or moreorganic impurities. More particularly, treatment of the waste stream(i.e., feed) by membrane separation forms a retentate enriched inorganic phosphorus compounds and salt impurities relative to thepermeate and the feed stream comprises at least a portion of theretentate. These organic phosphorus compounds typically include, forexample, N-formyl-N-(phosphonomethyl)glycine,N-methyl-N-(phosphonomethyl)glycine, aminomethylphosphonic acid, methylaminomethylphosphonic acid, iminodiacetic acid, and combinationsthereof. The permeate typically contains various organic impurities(e.g., formic acid and/or formaldehyde).

Again with reference to FIG. 1, evaporation, or concentration of wastestream 1 provides an aqueous waste slurry 13 that is introduced into avessel 17 suitable for heating of the slurry for oxidation of organiccarbon and phosphorus-containing species (e.g., to form phosphate andpyrophosphate species).

Although shown in FIG. 1, it is to be understood that concentration offeed stream 1 is not required for operation of the processes of thepresent invention. Thus, in various embodiments, feed stream 1 isintroduced directly to vessel 17 for oxidation of one or more compoundscontaining organic carbon and phosphorus. However, concentration of feedstream 1 is generally preferred as concentration of the feed streamreduces energy requirements during and simplifies subsequent processing(e.g., oxidation of phosphorus and organic carbon). Thus, concentrationof at least a portion of the aqueous feed stream is generally preferredin connection with commercial-scale recovery processes.

Generally in accordance with the present invention, and in accordancewith the embodiment depicted in FIG. 1, vessel 17 is a suitableapparatus for calcination of aqueous waste slurry 13 or combustion ofcomponents of the aqueous waste slurry 13. The precise configuration ofvessel 17 is not narrowly critical and may be readily selected by oneskilled in the art.

For example, in various preferred embodiments, vessel 17 is in the formof a rotary kiln, or calciner. Calcination of aqueous waste slurry 13generally proceeds by contacting the vessel, or calciner with a heatsource 19 for heating of the aqueous waste slurry therein and, as shownin FIG. 1, introducing gas stream 21 into vessel 17. Generally, gasstream 21 comprises an oxygen-containing gas (e.g., air) and,additionally or alternatively, may comprise a fuel such as, for example,propane or natural gas.

In various other embodiments, gas stream 21 is introduced into vessel 17for oxidizing one or more compounds containing phosphorus and organiccarbon in the absence of direct heating of vessel 17. Thus, in suchembodiments, oxidation of the components of the aqueous waste slurryproceeds via combustion of the components of the feed stream in theabsence of calcination of the slurry by direct heating of vessel 17.

Regardless of the precise manner of operation, heating or combustingcomponents of the aqueous feed stream or slurry removes various organicimpurities from the feed stream including, for example, in overheadsstream 23.

Oxidizing one or more compounds containing phosphorus and organic carbonin vessel 17 produces a phosphate-containing cake 25 that is introducedinto an acidification zone within an acidification vessel 29 into whichan acidic liquid medium 33 is also introduced. Typically, the acidicliquid medium comprises an acid (e.g. hydrochloric acid) at aconcentration of at least about 10 wt. %, more typically at least about20 wt. % and, still more typically, at least about 35 wt. %.

Contacting phosphate-containing cake 25 with the acidic liquid medium 33within the acidification zone produces a solution 37 comprising at leastone inorganic salt and phosphoric acid. In various embodiments, thesolution formed in the acidification zone comprises sodium chloride.

Solution 37 produced in the acidification zone is introduced into aconcentration vessel 41 for removal of water 45 and precipitation ofsalt crystals from the solution. Precipitation of salt crystals withinvessel 41 forms an aqueous product mixture 49 comprising the saltcrystals and a mother liquor comprising phosphoric acid. Precipitationof salt crystals generally comprises removal of water from solution 37by, for example, heating the product mixture. More particularly, removalof water from solution 37 typically comprises heating the solution totemperatures in excess of at least about 50° C., or at least about 80°C.

Aqueous product mixture 49 is introduced into separator 53 forseparation of the aqueous product mixture into a salt crystal fraction57 and an aqueous mother liquor fraction 61. Separation of the saltcrystals and phosphoric acid-containing mother liquor of aqueous productmixture 49 generally proceeds in accordance with suitable solids-liquidseparation methods known in the art including, for example,centrifugation.

The salt crystals thus produced are generally suitable for use in avariety of applications (e.g., chloro-alkali processes). Certainapplications may require a salt product of certain minimum purity asdetermined by one or more properties of the salt product including, forexample, TOC content, total nitrogen content, and/or total phosphatecontent. Again with reference to FIG. 1, salt product crystals 57 areoptionally introduced into washing vessel 65 into which is alsointroduced a suitable washing medium 69 to produce a purifiedsalt-containing product 73. Typically, the washing medium is water, orbrine water and the salt crystals are washed via counter-current flow ofthe crystals and washing medium within washing vessel 65. The precisecomposition of the washing medium and the manner of washing of the saltcrystals are not narrowly critical and may be readily selected by oneskilled in the art.

Although shown in FIG. 1, it is to be understood that washing of thesalt crystals is not required in accordance with the processes of thepresent invention. That is, though a washing operation is typicallyutilized, suitable salt products may be provided in the absence of awashing operation. Regardless of any washing operation, preferably thesalt product (e.g., purified salt-containing product) exhibits one ormore properties. For example, in various preferred embodiments, the saltproduct generally exhibits a TOC content of no more than about 50 ppm,or no more than about 40 ppm, typically no more than about 30 ppm, moretypically no more than about 20 ppm and, still more typically, no morethan about 10 ppm. Additionally or alternatively, the salt productgenerally exhibits a total nitrogen content of no more than about 50ppm, or no more than about 35 ppm, typically no than about 18 ppm and,still more typically, no more than about 10 ppm. Further in accordancewith the present invention, the salt product generally exhibits a totalphosphate content of no more than about 500 ppm, typically no more thanabout 380 ppm, more typically no more than about 250 ppm and, still moretypically, no more than about 100 ppm.

Again with reference to FIG. 1, purified salt-containing product 73 mayoptionally be introduced into vessel 77 and combined with aqueous medium81 also introduced into vessel 73 to produce a brine solution 85.Generally, the brine solution exhibits a total solids/salt content of atleast about 5 wt. %, at least about 10 wt. %, or at least about 20 wt.%. Typically, the total solids/salt content of the brine solution isfrom about 5 to about 45 wt. %, more typically from about 10 to about 35wt. % and, still more typically, from about 20 to about 30 wt. %. Brinesolution produced in accordance with the processes of the presentinvention is suitable for use in a variety of applications including,for example, in chloro-alkali processes for conversion of sodiumchloride to sodium hydroxide and chlorine.

Further in accordance with the present invention, phosphoric acid isrecovered from aqueous mother liquor fraction 61. As shown in FIG. 1,mother liquor fraction 61 is introduced into an extraction zone withinan extraction vessel 89 and contacted and mixed with an extractionsolvent 93. The composition of the extraction solvent is not narrowlycritical. Typically, however, the extraction solvent is an organicsolvent comprising, for example, tributyl phosphate, diisopropyl ether,and combinations thereof. In various embodiments, the organic solventcontains from about 10 wt. % to about 20 wt. % tributyl phosphate andfrom about 80 wt. % to about 90 wt. % diisopropyl ether. In accordancewith these and various other embodiments, the mass ratio of the organicsolvent to the mother liquor fraction in the extraction zone isgenerally from about 1:1 to about 5:1, or from about 2:1 to about 3:1.Mixing the mother liquor fraction and organic solvent forms anextraction mixture comprising an organic extract comprising phosphoricacid and an aqueous raffinate depleted in phosphoric acid relative tothe mother liquor fraction. The organic extract 97 is separated from theaqueous raffinate 101. Although not shown in FIG. 1, at least a portionof aqueous raffinate 101 may be introduced into acidification vessel 29.

In this manner, an organic extract 97 comprising a substantial portionof the phosphoric acid of the mother liquor fraction is formed. Moreparticularly, in accordance with the present invention, the organicextract typically comprises at least about 5 wt. %, more typically atleast about 10 wt. %, and preferably at least about 15 wt. % of thephosphoric acid contained in the mother liquor fraction.

Additionally or alternatively, it is to be understood that recovery ofphosphorus values can be indicated by the phosphate ion concentration ofthe mother liquor fraction. More particularly, in various embodimentsthe phosphate ion content of the mother liquor fraction and/or organicextract comprising phosphoric acid represents a phosphate recovery of atleast about 10 wt. %, more typically of at least about 20 wt. %, andstill more typically of at least about 30 wt. %.

The precise configuration of extraction vessel 89 is not narrowlycritical, but is typically selected to be suitable for countercurrent,liquid-liquid extraction for recovery of phosphoric acid from motherliquor fraction 61.

Again with reference to FIG. 1, organic extract 97 comprising phosphoricacid is introduced into a stripping zone within a stripping vessel 105along with an aqueous medium 109 to form a mixture (e.g., stripping zoneextraction mixture) comprising an aqueous extract comprising phosphoricacid and an organic raffinate depleted in phosphoric acid. The organicraffinate depleted in phosphoric acid 113 is separated from aqueousextract 117. Although not shown in FIG. 1, at least a portion of organicraffinate 113 may be introduced into extraction vessel 89.

In various embodiments, the aqueous, solids-depleted mother liquorfraction 61 may comprise one or more metallic impurities selected fromthe group consisting of arsenic, copper, zinc, iron, nickel, manganese,aluminum, chromium, and combinations thereof. Although not shown in FIG.1, in various embodiments one or more metallic impurities may be removedfrom aqueous mother liquor fraction 61 prior to its introduction intoextraction vessel 89.

One suitable method for removal of metallic impurities from the aqueous,solids-depleted mother liquor fraction comprises ion exchange. Inaccordance with various embodiments, the solids-depleted mother liquorfraction is contacted with an ion exchange resin selective for removalof one or more metallic impurities therefrom to form a solids-depletedmother liquor fraction having a reduced concentration of the one or moremetallic impurities. Contact of the mother liquor fraction with the ionexchange resin generally comprises passing the mother liquor fractionthrough a bed of ion exchange resin within a suitable vessel. Theprecise configuration of the ion exchange resin and vessel are notnarrowly critical and may readily be selected by one skilled in the art.Suitable ion exchange resins include, for example and withoutlimitation, Amberlite IRA-120 resin manufactured by Rohm and Haas,(Philadelphia, Pa.) and Dowex IDA-1 (Iminodiacetic acid) resinsavailable from the Dow Chemical Company (Midland, Mich.).

Additionally or alternatively, removal of metallic impurities from theaqueous, solids-depleted mother liquor fraction may comprise introducinga source of sulfide anions (e.g. hydrogen sulfide or sodiumhydrosulfide) into the mother liquor fraction to form an insoluble metalsulfide fraction comprising one or more metal sulfides (e.g., arsenicand/or copper sulfide). The insoluble metal sulfide fraction isseparated from the solids-depleted mother liquor fraction to form asolids-depleted mother liquor fraction having a reduced concentration ofone or more metallic impurities for further processing (e.g.,liquid-liquid extraction) and recovery of phosphoric acid therefrom. Themanner of contact of the mother liquor fraction with the source ofsulfide anions is not narrowly critical and a suitable vessel andconfiguration may be readily selected by one skilled in the art. Theprecise composition of the source of sulfide anions is likewise notnarrowly critical and may be readily selected by one skilled in the artdepending, for example, on the composition of the mother liquorfraction, the metals to be removed, and the desired metal impuritycontent specification.

FIG. 2 depicts another embodiment of a recovery process of the presentinvention utilizing direct combustion to oxidize organic carbon andphosphorus-containing components of the aqueous waste stream. Feedstream 101 comprising components of the aqueous waste stream isintroduced into and passed through atomizing nozzle 105 to form anatomized aqueous waste stream 109 that is discharged into a combustionchamber 113.

Organic carbon and phosphorus-containing impurities contained in theatomized aqueous waste stream 109 are combusted along with a fuel source117 in the presence of oxygen to form a combustion gas stream 121comprising carbon dioxide, phosphorus oxide and particulate saltimpurities. Typically, the combustion or flame temperature withincombustion chamber 113 is maintained at about 500° C. or higher, moretypically at least about 600° C. and, still more typically, at leastabout 700° C. Preferably, the combustion or flame temperature ismaintained at from about 500° C. to about 1000° C., and more preferablyfrom about 700° C. to about 900° C. or from about 600° C. to about 800°C.

Particulate salt impurities 125 are separated from the combustion gasstream 121 and the combustion gas stream depleted in particulate saltimpurities 129 is introduced into a scrubbing vessel 131. An aqueousscrubbing liquid 137 is also introduced into scrubbing vessel 131 toproduce a stream of phosphoric acid 141.

In accordance with the embodiment depicted in FIG. 2, particulate saltimpurities may satisfy, or may be further processed as detailedelsewhere herein (e.g., by washing) to exhibit one or more of theabove-noted properties of TOC content, total nitrogen content, and/ortotal phosphate content. In addition, particulate salt impurities may beincorporated into brine solutions as described elsewhere herein.

B. Recovery of Glyphosate

As noted, processes of the present invention are suitable for recoveryof phosphorus values and salt impurities from aqueous waste streamsgenerated in the manufacture of glyphosate and other phospho-herbicides.To aid in recovery of these components and improve overall economicsglyphosate or other valuable components are recovered from the feedstream comprising components of the aqueous waste stream prior torecovery of phosphorus values and salt impurities by one or moremembrane separation and/or ion exchange operations.

FIG. 3 depicts one embodiment of a process for recovery of glyphosatethat may be utilized in conjunction with the phosphorus value—saltimpurity recovery processes detailed elsewhere herein. As shown, anaqueous process stream 301 is introduced into a membrane separation unit305 containing a suitable separation membrane. Contacting the aqueousprocess stream 301 with the separation membrane forms a retentate 309and a permeate 313. The retentate comprises glyphosate or a salt thereofand, more particularly, is typically enriched in glyphosate relative tothe permeate and may be concentrated and recovered as product. Furtherin accordance with such embodiments, the feed stream (e.g., feed streams1 and 101 shown in FIGS. 1 and 2, respectively) comprises at least aportion of the permeate.

Although not shown in FIG. 3, an optional dilution/diafiltration streammay be introduced into membrane separation unit 305 such that themembrane operates as a diafiltration membrane. Additionally oralternatively, aqueous process stream 301 may be diluted by combinationwith a suitable aqueous medium prior to introduction into membraneseparation unit 305 such that the separation membrane operates as adiafiltration membrane.

Generally, in accordance with the present invention, any of a variety ofmembrane separation techniques well-known in the art may be utilizedincluding, for example, ultrafiltration, microfiltration,nanofiltration, and reverse osmosis. However, in various preferredembodiments, the process of the present invention utilizesnanofiltration.

The membrane separation unit 305 may be configured as either a singlepass or multi-pass system and may comprise one or more ultrafiltration,microfiltration, nanofiltration and/or reverse osmosis membranes ormodules. The membrane modules may be of various geometries and includeflat (plate), tubular, capillary or spiral-wound membrane elements andthe membranes may be of mono- or multilayer construction. In someembodiments, tubular membrane modules may allow a higher solids contentin the mother liquor solution to be treated such that solids reductionupstream of the membrane separation unit is not required.

In order to adequately withstand the often relatively low pH conditionsprevailing in the solids-depleted mother liquor fraction fed to themembrane separation unit, the separation membranes and other components(e.g., support structure) of the membrane modules are preferablyconstructed of suitably acid-resistant materials.

Suitable nanofiltration separation membranes are typically constructedof organic polymers such as crosslinked aromatic polyamides in the formof one or more thin film composites. Generally, suitable nanofiltrationmembranes exhibit a Molecular Weight Cut Off (MWCO) of from about 150daltons to about 1000 daltons and, typically, of about 250 daltons. Inaddition to the size (e.g., largest dimension) of process streamcomponents or constituents, separation by suitable nanofiltrationmembranes also typically includes a component based on the charge of themembrane, which depends, at least in part, on the pH of the processstream contacted with the membrane. Examples of suitable nanofiltrationmembranes include, for example and without limitation, the Desalmembranes (e.g., Desal-5 DK and Desal KH) available from GE OsmonicsIncorporated, a subsidiary of GE Infrastructure (Minnetonka, Minn.), theNF membranes (e.g., NF 40, NF 40HF, NF 50, NF 70, and NF 270) availablefrom FilmTec Corporation, a subsidiary of the Dow Chemical Company(Midland, Mich.), MPS-34 membrane available from Koch Membranes(Wilmington, Mass.), SU 600 membrane available from Toray (Japan), andthe NTR membranes (e.g. NTR 7450 and NTR 7250) available from NittoElectric (Japan). Suitable reverse osmosis membranes include, forexample and without limitation, SE-type reverse osmosis membranesavailable from GE Osmonics Incorporated (Minnetonka, Minn.) and SW30reverse osmosis membranes available from FilmTec Corporation.

Suitable nanofiltration membranes typically exhibit the followingrejection characteristics with respect to chloride ions and glyphosate,as determined from compositional data for the initial process stream andresulting retentate and permeate. These compositional data may bedetermined by methods known in the art including, for example, highperformance liquid chromatography (HPLC) and mass spectrometry analysis.A rejection characteristic may be defined as the difference between oneand the ratio of permeate concentration (Cp) of a component to theaverage of the process stream concentration (Cs) and retentateconcentration (Cr) of the component: 1−Cp/((Cs+Cr)/2). Suitablenanofiltration membranes generally exhibit a rejection characteristicwith respect to chloride ions of from about 30% to about 100%, typicallyfrom about 40% to about 80% and, more typically, of about 40% to about50%. The glyphosate rejection characteristic of suitable nanofiltrationmembranes is generally from about 75% to about 100%, typically fromabout 90% to about 98% and, more typically, about 95%.

Nanofiltration and reverse osmosis are pressure-driven separationprocesses driven by the difference between the operating pressure andthe osmotic pressure of the solution on the feed or retentate side ofthe membrane. The operating pressure in the membrane separation unit 305will vary depending upon the type of membrane employed, as osmoticpressure is dependent upon the level of transmission of solutes throughthe membrane. Operating pressures in membrane separation unit 305 aresuitably achieved by passing the incoming aqueous process stream 301through one or more pumps (not shown) upstream of the membrane unit, forexample, a combination booster pump and high-pressure pump arrangement.Generally, nanofiltration operations exhibit lower osmotic pressuresthan reverse osmosis operations, given the same feed solution. For themembranes that were tested, the osmotic pressure for nanofiltration ofglyphosate product mother liquor solutions was typically from about 3000kilopascals (kPa) absolute to about 6500 kPa absolute and more typicallyfrom about 3000 kPa to about 5500 kPa. The operating pressure necessaryto achieve adequate water removal in permeate 313 is significantly lowerin the case of nanofiltration membranes as compared to reverse osmosismembranes. The driving force for transmission of water through themembrane (i.e., permeate flux) increases with the operating pressure.However, the benefits of increased operating pressure must be weighedagainst the increased energy requirements (e.g. energy required forpumping) and the detrimental effects on membrane life (i.e.,compaction).

In order to maintain or enhance membrane separation efficiency andpermeate flux, the membranes should be periodically cleaned so as toremove contaminants from the surface of the membrane. Suitable cleaningincludes cleaning-in-place (CIP) operations wherein the surface of themembrane is exposed to a cleaning solution while installed withinmembrane separation unit 305. Preferred systems monitor the conductivityof permeate 313 as conductivity can be correlated to the concentrationof N-(phosphonomethyl)glycine product and other components that passthrough the membrane. An increase in conductivity in the permeate mayindicate an increase in transmission of the N-(phosphonomethyl)glycineproduct through the membrane and can be used to signal the need forcleaning operations. Additionally, a fall in permeate flow with allother factors remaining constant may indicate fouling and the need forcleaning operations.

Cleaning protocols and cleaning solutions will vary depending on thetype of separation membrane employed and are generally available fromthe membrane manufacturer. Suitable cleaning solutions may include, forexample, caustic or alkaline solutions. For example, in the case ofpolyamide thin-film based reverse osmosis membranes, suitable cleaningsolutions may include membrane cleaners available from GE Betz, Inc., asubsidiary of GE Infrastructure (Trevose, Pa.), such as (1) an alkaline,water-soluble surfactant-containing membrane cleaner that removesorganic foulants and comprising diethanolamine, the trisodium salt ofnitrilotriacetic acid, the trisodium salt of N-hydroxyethylenediaminetriacetic acid, triethanolamine, monoethanolamine and sulfonated sodiumsalts of 1,1′-oxybis, tetrapropylene benzene derivatives; and/or (2) analkaline chelating agent-containing membrane cleaner comprisingtrisodium phosphate (sodium phosphate, tribasic), the disodium salt ofsilicic acid (sodium metasilicate), sodium carbonate and sodiumdodecylbenzenesulfonate. In order to not damage the membranes andunnecessarily shorten membrane life, the CIP operation is preferablyconducted using a solution of a standard pH at pressure and temperatureconditions known to those skilled in the art. In some applications, itmay be advantageous to conduct a cleaning operation on new separationmembranes prior to use in the membrane separation operation in order toimprove membrane performance.

Again with reference to FIG. 3, retentate 309 may optionally (as denotedby the dashed lines in FIG. 3) be introduced into an ion exchange columnor unit 313 containing an ion exchange zone comprising a bed of ionexchange resin. Retentate 309 is contacted with at least one ionexchange resin contained therein for selective removal of glyphosate toform an ion exchange zone effluent 317 depleted in glyphosate relativeto the retentate. Further in accordance with such embodiments, the feedstream (e.g., feed streams 1 and 101 shown in FIGS. 1 and 2,respectively) may comprise at least a portion of the ion exchange zoneeffluent. For example, a feed stream comprising at least a portion ofthe ion exchange effluent may be introduced into concentration vessel 5shown in FIG. 1, or may be introduced directly into vessel 17 foroxidation of one or more compounds containing organic carbon andphosphorus. Once the adsorption capacity of the ion exchange resin isdiminished (e.g., as determined by break-through of glyphosate), the bedmay be regenerated by means known in the art to desorb glyphosateproduct. Further in this regard, it is to be noted that in connectionwith aqueous waste streams from manufacture of glyphosate by the glycineprocess, ion exchange may be utilized to remove hydroxymethylphosphonicacid (HMPA) from the waste stream to form a feed stream for thephosphorus value—salt impurity recovery processes of the presentinvention.

Further in accordance with the present invention and with reference toFIG. 4, glyphosate may be recovered from an aqueous process stream by aprocess comprising at least one ion exchange operation followed by atleast one membrane separation operation. As shown in FIG. 4, aqueousprocess stream 401 is introduced into an ion exchange unit 405containing an ion exchange zone comprising a bed of ion exchange resinfor selective removal of glyphosate and/or one or more impurities (e.g.,HMPA). Waste stream 401 is contacted with the ion exchange resin to forman ion exchange zone effluent 409 comprising components of the aqueouswaste stream and depleted in glyphosate relative to the waste stream. Inaccordance with such embodiments, typically the feed stream of thephosphorus value—salt impurity recovery process (e.g., feed streams 1and 101 shown in FIGS. 1 and 2, respectively) may comprise at least aportion of the ion exchange zone effluent 409. The bed may likewise beregenerated by means known in the art to desorb glyphosate product.

Also in accordance with the embodiment depicted in FIG. 4, ion exchangeeffluent 409 is optionally (as depicted by dashed lines) introduced intoa membrane separation unit 413 and contacted with at least oneseparation membrane to form a retentate 417 and a permeate 421.Retentate 417 comprises glyphosate or a salt thereof and is enriched inglyphosate relative to the permeate and may be concentrated andrecovered as product. In accordance with such embodiments, the feedstream of the phosphorus value—salt impurity recovery process (e.g.,feed streams 1 and 101 shown in FIGS. 1 and 2, respectively) maycomprise at least a portion of the permeate 421.

FIG. 5 depicts another embodiment of a process for recovery ofglyphosate that may be utilized in conjunction with the phosphorusvalue—salt impurity recovery processes detailed elsewhere herein. Asshown, an aqueous process stream 501 is introduced into a first membraneseparation unit 505 containing a suitable separation membrane.Contacting the aqueous process stream 501 with the separation membraneforms a first retentate 509, which may be recovered as product, and afirst permeate 513. First retentate 509 comprises glyphosate or a saltthereof and, more particularly, is typically enriched in glyphosaterelative to first permeate 513. First permeate 513 is introduced into asecond membrane separation unit 517 comprising a suitable separationmembrane to form a second retentate 521 and a second permeate 525.Second retentate 521 is typically enriched in glyphosate or a saltthereof relative to second permeate 525. The feed stream of thephosphorus value—salt impurity recovery process (e.g., feed streams 1and 101 shown in FIGS. 1 and 2, respectively) may comprise at least aportion of second retentate 521.

Again with reference to FIG. 5, first retentate 509 is optionally (asindicated by the dashed lines in FIG. 5) introduced into an ion exchangezone within an ion exchange column or unit 529 containing a bed of ionexchange resin. First retentate 509 is contacted with at least one ionexchange resin contained therein for selective removal of glyphosatetherefrom to form an ion exchange zone effluent 533 depleted inglyphosate relative to first retenate 509. In accordance with variousembodiments, the feed stream of the phosphorus value-salt impurityrecovery process (e.g., feed streams 1 and 101 shown in FIGS. 1 and 2,respectively) may comprise at least a portion of ion exchange zoneeffluent 533.

In accordance with various preferred embodiments generally depicted inFIG. 5, the first membrane separation unit comprises a nanofiltrationmembrane. Further in accordance with such embodiments, the secondmembrane separation unit comprises a reverse osmosis membrane.

In various embodiments of the process depicted in FIG. 5, water isremoved from first permeate 513 in an optional concentration operation(not shown) prior to its introduction into second membrane separationunit 517.

C. Recovery of PMIDA

As noted, various embodiments of the present invention are directed torecovery of phosphorus values and salt impurities from aqueous streamscomprising one or more phospho-herbicide precursors. For example,various embodiments of the present invention are directed to recovery ofPMIDA from aqueous process streams generated in the manufacture ofglyphosate. It is to be understood that the processes described above inconnection with FIGS. 3, 4, and 5 including membrane separation and/orion exchange operations are suitable for recovery of PMIDA generally inaccordance with the above discussion.

D. Glufosinate Production and Recovery

The processes of the present invention are likewise suitable forrecovery of phosphorus values and salt impurities from aqueous wastestreams generated in the manufacture of glufosinate. A variety ofprocesses for preparation of glufosinate are known in the art. Many ofthese processes utilize phosphorus-containing compounds (e.g., PCl₃) andbasic compounds (e.g., sodium hydroxide and/or potassium hydroxide). Atleast in part because these routes for the preparation of glufosinatetypically utilize phosphorus trichloride, salt and phosphorus containingwaste streams are typically generated. It is currently believed thatvarious aqueous waste streams generated in the manufacture ofglufosinate (e.g., the mother liquor resulting from preparation ofglufosinate wet cake) include phosphorus and salt impurities that may berecovered by the processes of the present invention described above.

Various methods known in the art prepare glufosinate via routes thatutilize phosphorus trichloride to form an ethyl vinylphosphinateprecursor. The ethyl vinylphosphinate precursor is subjected tohydroformylation-aminocarbonylation, followed by hydrolysis to produceglufosinate.

In particular, one method of producing glufosinate generally comprisesconverting phosphorus trichloride to methylphosphonous dichloride or itsderivatives. The methylphosphonous dichloride or derivatives may bereacted directly with methanol to form methyl methylphosphinate. Methylmethylphosphinate may then be reacted with vinylic compounds (e.g. vinylacetate) to form an intermediate compound (e.g.,acetoxyethyl)phosphinate). The resulting intermediate is pyrolyzed toprepare the requisite ethyl vinylphosphinate precursor. The ethylvinylphosphinate precursor is subjected tohydroformylation-aminocarbonylation, followed by hydrolysis of thehydroformylation-aminocarbonylation product in the presence ofhydrochloric acid to produce glufosinate.

Alternatively, another method of producing glufosinate generallycomprises converting phosphorus trichloride to an adduct ofmethylphosphonous trichloride and aluminum tetrachloride (i.e.,CH₃PCl₃.AlCl₄). The adduct may be reacted with ethylene to form anintermediate adduct, which then may be reacted with ethanol to formethyl 1-(2-chloroethyl)-methylphosphinate. Ethyl1-(2-chlroethyl)-methylphosphinate may then be reacted with potassiumhydroxide and ethanol to prepare the requisite ethyl vinylphosphinateprecursor. The ethyl vinylphosphinate precursor is subjected tohydroformylation-aminocarbonylation, followed by hydrolysis of thehydroformylation-aminocarbonylation product in the presence ofhydrochloric acid to produce glufosinate.

E. Supercritical Treatment

Certain embodiments of the present invention are directed to processesfor recovery of salt impurities, or salt values from aqueous wastestreams generated in the manufacture of phospho-herbicides or precursorsthereof that generally comprise subjecting the aqueous waste stream totemperature and pressure conditions sufficient to convert water in theaqueous waste stream into supercritical water. The aqueous waste streamstreated in these embodiments typically comprise one or more saltimpurities, one or more organophosphorus compounds, and various otherorganic compounds. In various preferred embodiments, the process isutilized for recovery of salt values from an aqueous process streamgenerated in the manufacture of glyphosate.

It is known that at extremely high temperatures and pressures, theliquid and gaseous phases of water and other fluids becomeindistinguishable. In water, the critical point occurs at around 647 K(374° C. or 705° F.) and 22.064 MPa (3200 psia or 218 atm). Under thesesupercritical temperature and pressure conditions, water becomes a densegas having a density between that of water vapor and liquid water atstandard conditions, and exhibiting unique properties. For example,solubility behavior is reversed in supercritical water causing salts toprecipitate out of solution so that they can be handled and treatedusing conventional methods for solid-waste residuals. More generally,polar, ionic compounds are not soluble in supercritical water.Accordingly, converting water in the aqueous waste stream tosupercritical water results in precipitation of various ionic componentsof the waste stream to form a particulate impurity product within thesupercritical treatment reactor or vessel. For example, various saltimpurities (e.g., sodium chloride) precipitate from the aqueous wastestream under supercritical conditions. Other ionic compounds present inthe waste stream include salts of phospho-herbicides and precursorsthereof, which also precipitate from the aqueous process stream undersupercritical conditions. For example, in the case of aqueous wastestreams generated in the manufacture of glyphosate, the aqueous processstream typically comprises one or more glyphosate salts and/or one ormore salts of PMIDA. Thus, in accordance with salt recovery processembodiments of the present invention in which the aqueous waste streamis generated in the manufacture of glyphosate, a solid precipitatecomprising salt impurities, salts of glyphosate, and/or salts of PMIDAis formed. Precipitation and recovery of salts from the aqueous wastestream provides a purified, or treated waste stream generally depletedin salt impurities, and also typically depleted in organic phosphoruscompounds relative to the composition of the aqueous waste stream.

In addition to the ionic components, the aqueous waste stream maycomprise various non-ionic organic compounds. For example, in the caseof aqueous waste streams generated in the manufacture of glyphosate, theaqueous waste stream typically comprises formaldehyde and/or formicacid. Removal of formaldehyde and formic acid from such aqueous wastestreams typically comprises the catalyzed oxidation of formaldehyde toform formic acid, and the further oxidation of formic acid to carbondioxide and water. It is currently believed that subjecting the aqueouswaste stream to supercritical conditions results in oxidation offormaldehyde and/or formic acid impurities to carbon dioxide and waterdue to the presence of oxygen or other dissolved oxidizer in the aqueouswaste stream. That is, conditions suitable for the oxidation of thesenon-ionic organic components generally prevail within the supercriticaltreatment reactor. Oxidation of these non-ionic components of theaqueous waste stream results in a purified aqueous waste stream depletedin such components relative to the aqueous waste stream.

Generally, the aqueous waste stream is introduced into a suitablereactor or vessel comprising a supercritical treatment zone within whichthe prevailing temperature and pressure conditions are at or above thesupercritical temperature and pressure of water. The manner of operationof the reactor or vessel for subjecting the waste stream tosupercritical treatment conditions is not narrowly critical. Forexample, in various embodiments, the supercritical treatment reactor isoperated as a batch reactor, while in other embodiments the reactor isoperated as a continuous reactor or vessel. An aqueous waste streamunder ambient temperature and pressure may be introduced into acontinuous supercritical treatment reactor using a suitable apparatus toovercome the pressure at the inlet to the vessel (e.g., a pump havingsufficient operating pressure) and in a manner so as to not underminethe maintenance of supercritical conditions in the reactor. Additionallyor alternatively, the pressure and/or temperature of the aqueous wastestream may be increased during one or more pretreatment stages prior tointroduction into the supercritical treatment reactor to provide anaqueous waste stream under temperature and pressure conditions nearerthe supercritical conditions.

Generally, the aqueous waste stream is subjected to temperature andpressure conditions within the supercritical treatment zone sufficientto form supercritical water. It is currently believed that the varioussolutes present in the aqueous waste stream may impact the supercriticaltemperature and/or pressure of the aqueous waste stream. If necessary,one skilled in the art can readily estimate or determine the impact ofthe solutes on the supercritical temperature and pressure to determineappropriate operating temperatures and pressures to be maintained in thesupercritical treatment zone.

Regardless of the precise impact of solutes on supercritical temperatureand/or pressure, typically the aqueous waste stream is subjected totemperature and pressure in excess of the supercritical temperature andpressure of water. Generally, the aqueous waste stream is subjected to atemperature of at least about 375° C., typically at least about 400° C.and, more typically, at least about 425° C. Generally, the aqueous wastestream is subjected to a pressure of at least about 22 MPa, typically atleast about 25 MPa and, more typically, at least about 30 MPa.

The residence time of the aqueous waste stream within the supercriticaltreatment zone of the reactor (i.e., the time the aqueous waste streamis subjected to supercritical temperature and pressure conditions) isgenerally at least about 5 minutes, at least about 15 minutes, or atleast about 30 minutes. Typically, the aqueous waste stream is subjectedto supercritical temperature and pressure conditions for from about 5 toabout 180 minutes, more typically for from about 15 to about 150 minutesand, still more typically, for from about 30 to about 120 minutes.

As noted, subjecting the waste stream to supercritical temperatures andpressures yields a mixture comprising precipitated salt crystals and apurified aqueous waste stream. Further, in accordance with the presentinvention, precipitated salt crystals may be recovered from thismixture. For example, to facilitate recovery of precipitated saltcrystals, the supercritical treatment reactor may have a tapered, orcone-shaped bottom to facilitate gravity separation and collection ofprecipitated salt crystals. Additionally or alternatively, precipitatedsalt crystals may be recovered from this mixture using methods generallyknown in the art, e.g., centrifugation, filtration, etc.

The recovered salt crystals may be disposed of in accordance withvarious methods known in the art including, for example, introductioninto a landfill. Additionally or alternatively, precipitated saltcrystals may be utilized in any of the processes for recovery of saltimpurities and phosphorus values detailed elsewhere herein. In variousembodiments, the precipitated salt crystals are recovered in the form ofa slurry suitable for use in the phosphorus value—salt impurity recoveryprocesses of the present invention. However, if necessary, theprecipitated salt crystals may be slurried in a suitable aqueous medium,for example to facilitate further processing (e.g., pumping).

Since salt impurities have been removed from the aqueous waste stream byprecipitation, the purified aqueous waste stream is typically depletedin salt impurities relative to the aqueous waste stream subjected tosupercritical conditions. In addition, based on the oxidative conditionsto which the waste stream is subjected, the purified waste stream islikewise typically depleted in non-ionic organic components relative tothe aqueous waste stream. Generally, recovery of the purified aqueouswaste stream comprises venting of the vessel, or reactor. In view of therelatively high temperatures and pressures within the vessel, preferablypurified aqueous waste stream is recovered from the reactor utilizing amulti-stage process in which the pressure and temperatures are loweredin a step-wise manner by passage of the purified aqueous waste streamthrough suitable apparatus (e.g., one or more heat exchangers). Furtherin accordance with various preferred embodiments, the heat (i.e.,energy) recovered during one or more of the multiple recovery stages maybe utilized in heating and/or pressurizing the aqueous waste streamprior to its introduction into the vessel.

In various preferred embodiments, the recovered purified aqueous wastestream is in the form of a relatively pure aqueous waste stream suitablefor disposal or use as process water without any treatment. For example,the purified aqueous waste stream may be used as process water in thesalt recovery process detailed herein, in phosphorus value—salt impurityrecovery processes of the present invention, or elsewhere in themanufacture of phospho-herbicides. Various conventional processes formanufacture of phospho-herbicides subject recovered mother liquor tobiological treatment to provide an aqueous waste stream suitable fordisposal. The purified aqueous waste stream may likewise be subjected tosuch treatment, but it is currently believed that the biologicaltreatment may be operated at a higher throughput based on the relativelylow impurity content of the aqueous waste stream.

PMIDA or a salt thereof recovered in accordance with the recoveryprocesses detailed herein may be converted to glyphosate or a saltthereof in accordance with methods known in the art as described, forexample, in U.S. Pat. No. 6,417,133 to Ebner et al.; U.S. Pat. No.7,129,373 to Coleman et al.; U.S. Pat. No. 7,015,351 to Haupfear et al.;Wan et al. International Publication No. WO 2006/031938; Liu et al.International Publication No. WO 2005/016519; and Arhancet et al.International Publication No. WO 2006/089193; the entire contents ofwhich are incorporated herein by reference for all relevant purposes.Further in accordance with the present invention, precursors of PMIDArecovered by any of the processes detailed herein may be utilized inprocesses for preparation of glyphosate. For example, IDA recovered inaccordance with the present invention may be utilized to prepare PMIDAor a salt thereof in accordance with methods known in the art asdescribed, for example, in U.S. Pat. No. 7,329,778, the entire contentsof which are incorporated herein by reference for all relevant purposes.The PMIDA or a salt thereof may be converted to glyphosate or a saltthereof in accordance with the methods noted above.

Having described the invention in detail, it will be apparent thatmodifications and variations are possible without departing from thescope of the invention defined in the appended claims.

EXAMPLES

The following examples are included to demonstrate preferred embodimentsof the invention. It will be appreciated by those of skill in the artthat the techniques disclosed in the following examples representtechniques discovered by applicants to function well in the practice ofthe invention, and thus can be considered to constitute preferred modesfor its practice. However, those of skill in the art should, in light ofthe instant disclosure, also appreciate that many changes can be made inthe specific embodiments that are disclosed, while still obtaining likeor similar results, without departing from the scope of the invention.Thus, the examples are exemplary only and should not be construed tolimit the invention in any way. To the extent necessary to enable anddescribe the instant invention, all references cited are hereinincorporated by reference.

Example 1 Calcination of a Test Solution Representing Glyphosate MotherLiquor Under Acidic Conditions

This Example details calcination experiments utilizing a test solutionrepresenting acidic mother liquor formed during glyphosate manufacture.The experiments were undertaken to determine the effectiveness ofcalcination of the waste stream for conversion of organophosphoruscompounds and inorganic salts to solids comprising phosphate,pyrophosphate, and inorganic salts (e.g., sodium chloride).

The test solutions were prepared by combining mother liquor solutionsderived from crystallization of a product mixture generated duringlaboratory scale glyphosate production with other components to providea target solution composition. The aqueous test solutions generallycontained about 2 wt. % glyphosate, about 1 wt. % glycine, about 10 wt.% sodium chloride, phosphorous acid, and various other impurities (e.g.,glyphosine, NMG, HMPA, AMPA, PMIDA). The pH of the test solution wasapproximately 2.0. The composition of the test solution is set forth inTable 0.

TABLE 0 PMIDA wt % 0.19 Glyphosate wt % 1.97 IDA wt % 0.65 FM ppm 143 FAppm 224 Iminobis ppm 2655 NMG ppm 17419 PO₄ ppm 11584 NFG ppm 1072 AMPAppm 5305 Glycine ppm 3429 MAMPA ppm 3371 Chloride ppm 115656 H₃PO₃ ppm10176 FM = formaldehyde FA = formic acid

The experiments were conducted using a laboratory calcination/combustionsystem generally depicted in FIG. 2. Feed device 105 included aperistaltic pump and a stainless steel feeding tube for introduction offeed into combustion chamber 113. The tube of feed device 105 was incontact with an open flame within combustion chamber 113. Combustionchamber 113 was in the form of a stainless steel tank having a capacityof 1000 ml and a lip around the chamber to aid in retention of the solidand formation of a solid bed. The open flame within the combustionchamber was supplied by a natural gas torch positioned within thecombustion chamber. For heating of the combustion chamber, two Fisherburners (not shown in FIG. 2) were placed under the combustion chamberand the combustion chamber was rotated over the burners by a shaft andmotor arrangement (also not shown in FIG. 2) attached to the combustionchamber.

To conduct the experiments sodium chloride crystals (approx. 40 g) werecharged into the combustion chamber to serve as a solids bed, andaqueous test solution (approx. 40 g) was added to the solids bed.

The initial temperature of the combustion chamber was approximately90-150° C., and the temperature of the combustion chamber was slowlyraised until stabilized at approximately 750° C. Air was fed into thecombustion chamber at a rate of approximately 1 mL/min. After 10 minutesof heating the initial sample, additional test solution (approx. 40 g)was introduced into the combustion chamber. After the second addition oftest solution, the temperature inside the chamber was maintained above750° C. (e.g., at approx. 800° C.) for approximately 5 minutes. Duringheating of the initial test solution and the combined test solution,rotation of the combustion chamber was controlled at from approximately10 to 20 revolutions per minute (rpm). The solids remaining in thechamber were collected for analysis.

High performance liquid chromatography (HPLC), ³¹P Nuclear MagneticResonance (NMR), chloride titrations, and Total Organic Carbon (TOC)analyses were employed to analyze the recovered solids. The results ofthe ³¹P NMR analysis indicated only the presence of phosphate andpyrophosphate, but no organophosphorus compounds were identified. Theresults are shown in Table 1.

TABLE 1 Analytical Results for Solid Total Organic Total Total ContentNitrogen P₂O₇ ⁴⁻ PO₄ ³⁻ Total Cl⁻ insoluble (TOC) Content (wt %) (wt %)(wt %) (wt %) (ppm) (ppm) 0.75% 0.29% 58.61% 1.54% 346 13

These results indicate that calcination of the aqueous test solution issuitable for recovery of inorganic compounds from the test solutioncontaining organophosphorus compounds and inorganic salts.

Example 2 Direct Combustion of a Test Solution Representing GlyphosateMother Liquor Under Acidic Conditions

This Example details direct combustion experiments of an aqueous testsolution prepared as described in Example 1.

Sodium chloride crystals (approx. 67.4 g) were introduced into thecombustion chamber as a solids bed and test solution (approx. 40 g) wasintroduced into the solids bed. The temperature within the combustionchamber was increased until it reached at least approx. 750° C.

Additional test solution was introduced into the combustion chamberthrough a stainless steel nozzle. The outlet of the nozzle waspositioned directly above the flame of a propane torch within thecombustion chamber. Test solution was introduced into the combustionchamber at a rate of approximately 25 mL/min. Controlling the rate ofair flow and solution feed rate avoided accumulation of water from thetest solution passing through the flame collecting on the solids bed. Atotal of approx. 288.58 g of the test solution was introduced into thecombustion chamber at an approximately constant feeding rate (24.88mL/min). During introduction of the test solution into the flame, thetemperature within the combustion chamber was maintained atapproximately 800° C. The combustion chamber was allowed to cool to roomtemperature and the solids were recovered for analysis. The results areshown in Table 2. These results indicate the presence of phosphate andpyrophosphate species, but no organophosphorus compounds wereidentified.

TABLE 2 Analytical Results for Solid Total Total Total Organic NitrogenP₂O₇ ⁴⁻ PO₄ ³⁻ Total Cl⁻ insoluble Content Content (wt %) (wt %) (wt %)(wt %) (ppm) (ppm) 3.77% 0.95% 55.65% 1.02% 17 4

Example 3 Phosphoric Acid Recovery via Liquid-Liquid Extractions from aTest Solution Representing Sodium Chloride-Depleted Glyphosate MotherLiquor

This example details liquid-liquid extraction for recovery of phosphateions from a solution that may be prepared by calcination of a testsolution as described in Example 1. The test solution containedapproximately 73 wt. % PO₄ ³⁻ ions and approximately 3 wt. % sodiumchloride, balance water.

Test solution (approx. 50 g) and an organic solvent mixture (approx. 100g) of tributyl phosphate/isopropyl ether (15 wt. %/85 wt. %) were mixedin a beaker. Phase separation occurred after mixing for approximately 30minutes; the organic layer was separated from the aqueous phase by aseparation funnel. The organic layer contained about 14.5 wt. % PO₄ ³⁻.To this organic layer (117.8 g), water (approx. 12.75 g) was added andmixed for 15 minutes. After phase separation, the aqueous phase wasseparated and analyzed by HPLC. The aqueous phase contained approx. 46wt. % PO₄ ³⁻. The phosphate content of the recovered aqueous phaserepresented a phosphate recovery of approximately 35%.

Table 2A lists the starting composition of the solution and compositionsof the resulting phases.

TABLE 2A Centrifuge Moth. Liq. Organic Solvent Aqueous RaffinatePregnant Organic Phase % Fraction of Cent. (wt. and/or conc. of (wt.and/or conc. (wt. and/or conc. (wt. and/or conc. of Moth. LiquorComponents Component component) of component) of component)component)^(a) in Raffinate PO₃ ⁻³ 0.10 g (0.2%) 0 0.05 g (0.16%) 0.05 g(0.04%) 50.0 PO₄ ⁻³ 35.98 g (73.9%) 0 18.94 g (63.3%) 17.04 g (14.5%)52.6 Chloride 0.67 g (1.4%) 0 0.36 g (1.2%) 0.31 g (0.3%) 53.7 Sodium0.47 g (1.0%) 0 0.46 g (1.5%) 0.01 g (0.008%) 97.9 Aluminum 172 ppm 0279 ppm <1 ppm >99 Arsenic 83 ppm 0 62 ppm 19 ppm 46 Chromium 98 ppm 0144 ppm 4 ppm 90 Copper 78 ppm 0 99 ppm 7 ppm 78 Iron 127 ppm 0 102 ppm27 ppm 49 Manganese 81 ppm 0 129 ppm <1 ppm >98 Zinc 79 ppm 0 10 ppm 30ppm 8 Nickel 77 ppm 0 120 ppm 1 ppm 96 (n-Bu)₃PO 0 14.8 g (15%) 0^(b)17.8 g (12.6%) 0 (i-Pr)₂O 0 84.15 g (85%) 0^(b) 84.1 g (71.4%) 0 Total48.66 g 99.0 g 29.91 g 117.8 g N/A^(c) ^(a)Value for each componentobtained by subtracting the component weight in the raffinate from thecomponent weight in the centrifuge mother liquor. ^(b)No entrainment oforganic solvent in aqueous phase is assumed. ^(c)N/A = not applicableLaboratory Membrane Evaluation System

Experiments were undertaken to determine the suitability of membraneseparation techniques in connection with solids-depleted crystallizermother liquor solutions containing N-(phosphonomethyl)glycine, inorganicmonovalent and divalent salts, and various impurities, and at varyingpHs.

Laboratory membrane separation experiments were conducted using a setupshown schematically in FIG. 6, which allowed for the processing of thetest solutions at a variety of pH conditions. The laboratory evaluationsystem included a test solution feed vessel 601, two pumps 602 and 609,a membrane separation unit 622, and various process control equipmentincluding valves, pressure indicators, and temperature controllers.

The first pump 602 was a small centrifugal pump that was used as abooster pump. Booster pump 602 served two purposes. Primarily, thebooster pump provided a pressurized test solution feed stream 606 forhigh pressure pump 609. The booster pump also recycled a portion 604 ofthe test solution feed it removed from feed vessel 601 back to the feedvessel. This provided mixing of the contents of feed vessel 601. Feedvessel 601 was also equipped with an internal steam heating coil (notshown) that was used to keep the contents of the feed vessel at a givenset point temperature.

Pressurized test solution feed stream 606 from booster pump 602 waspressurized further by high pressure positive displacement pump 609(Wanner diaphragm pump) that was capable of generating approximately15.1 liters/min at 6996 kPa. A variable speed drive was installed on thepump drive to allow for feed flow rate control. High pressure pump 609was used to send a highly pressurized test solution feed stream 613 onto membrane separation unit 622.

Bench-scale spiral-wound membranes were tested in the laboratoryevaluation system. The operating pressure of the membrane separationunit was controlled by a throttle valve 630 positioned on the outletfrom which retentate 628 was withdrawn from membrane separation unit622. The operating pressures varied from about 3500 to about 6000 kPaabsolute, while the target operating pH was varied from a pH of about1.5 to a pH of about 10.0.

In all laboratory membrane separation experiments, retentate 628 wasrecycled to feed vessel 601 after it exited the housing of membraneseparation unit 622 in retentate recycle stream 650. The retentatepassed through a flow meter 635 that provided for monitoring of theretentate flow rate. The permeate 641 exiting the housing of membraneseparation unit 622 was also passed through a flow meter 636 thatprovided for monitoring of the permeate flow rate.

The permeate 641 could be diverted to a waste stream 643 or recycled tofeed vessel 601 in permeate recycle stream 646 depending upon the typeof experiment conducted. During operation in “recycle” mode, thepermeate was recycled to feed vessel 601 along with the retentate toprovide a constant test solution composition throughout the experiment.This mode of operation may be used to generate data regarding thestability of membrane flux and rejection characteristics. During a“batch concentration” experiment, the permeate would be diverted towaste, while the retentate was recycled to the feed vessel 601. Thistype of experiment allowed for the evaluation of membrane flux andrejection characteristics while the concentration of components, such asN-(phosphonomethyl)glycine and inorganic salts, in the test solutionfeed was increasing.

High performance liquid chromatography (HPLC) was employed to analyzethe process streams associated with the membrane separation experiments.A performance indicator known as a solute rejection characteristic wascalculated for each of the components of the test solution using thedata from the HPLC analysis. Solute rejection was defined as thedifference between one and the ratio of permeate concentration (Cp) fora component to the average of the process stream (Cs) and retentateconcentration (Cr): 1−Cp/((Cs+Cr)/2).

Example 4 Purification of a Test Solution with a Nanofiltration MembraneUnder Acidic Conditions (Diafiltration)

This example illustrates experiments conducted utilizing spiral-woundmembranes to assess the performance of a nanofiltration membrane toeffectively purify a test solution under acidic conditions when theseparation membrane is operated as a diafiltration membrane.

The performance of a polyamide thin-film based nanofiltration membranewith a nominal molecular weight cut off (MWCO) of 250 daltons availablefrom GE Osmonics was evaluated for use in connection with a testsolution having a pH of approximately 1.7. The test solution flow ratewas maintained at approximately 11.4 liters per minute, the operatingtemperature was maintained at about 40° C., and the operating pressurewas maintained at about 4826 kPa.

The test solution contained approx. 2 wt. % N-(phosphonomethyl)glycine,approx. 1 wt. % glycine, approx. 9 wt. % triethylamine hydrochloride andapprox. 3 wt. % hydrochloric acid. The test solution also containedother low level impurities typically seen in the process, such asglyphosine, NMG, HMPA, AMPA, PMIDA, and phosphorous acid. Approximately19.6 kg of the above-described material was diluted with approximately39 kg of deionized water to simulate operation of the separationmembrane as a diafiltration membrane.

The experiment was generally conducted in batch-concentration mode,wherein the retentate was continually recycled to the feed vessel whilethe permeate was removed from the system and collected in a separatevessel. However, prior to removal of each portion of the permeate (shownin Table 3 as percentage of initial test solution mass) the experimentwas conducted in recycle mode to stabilize the system. Feed, retentate,and permeate samples were collected throughout the experiment aspermeate was removed from the process. The results are reported in Table3 below.

TABLE 3 Experimental Testing to Assess Performance of a GE OsmonicsNanofiltration Membrane to Purify a Test Solution under AcidicConditions (Diafiltration) Permeate Removed as Permeate Flux ChlorideIons Percentage of (Gallons per ft² Rejection Remaining in Initial Testof membrane Characteristic - Test Solution Mass surface area perChloride Solution (%) day) Ions (%) (%) 0 20.4 46.1 100.0 12 18.6 45.193.0 24 17.4 46.9 85.3 37 15.6 47.0 76.7 48 12.6 45.8 68.5 70 6.0 39.648.5

As shown in Table 3, chloride ions can be effectively removed from thetest solution under acidic conditions when diafiltration is employed. Inaddition to evaluating membrane performance to separate chloride ionsfrom the test solution, it was also important to evaluate membraneperformance with regard to retention of glyphosate. Table 4 reportsglyphosate retention results.

TABLE 4 Experimental Testing to Assess Performance of a GE OsmonicsNanofiltration Membrane to Purify a Test Solution under AcidicConditions when Using Diafiltration Permeate Removed as Percentage ofRejection Glyphosate Ions Initial Test Characteristic - Remaining inTest Solution Mass (%) glyphosate (%) Solution (%) 0 94.0 100.0 12 94.399.2 24 94.3 98.2 37 94.2 97.1 48 94.0 95.8 70 91.2 91.3

As shown in Table 4, glyphosate was effectively retained under acidicconditions when diafiltration is employed. For example, after passage of70% of the initial test solution mass through the membrane, greater than90 wt. % of glyphosate originally in the test solution was found in theretentate while more than 50 wt. % of the chloride ions was found in thepermeate.

Example 5 Impact of Varying Alkaline Conditions on Performance of aNanofiltration Membrane

This example illustrates experiments conducted utilizing spiral-woundnanofiltration membranes to determine the impact of varying alkalineconditions when contacting a test solution with a nanofiltrationmembrane.

A polyamide thin-film based nanofiltration membrane with a nominalmolecular weight cut off (MWCO) of 250 daltons available from GEOsmonics was utilized in recycle mode to evaluate the impact of varyingpH, under alkaline conditions, on the performance of a nanofiltrationmembrane when contacting a test solution.

The test solution (pH 7.0) was prepared to meet the generalcompositional profiles in the process. The synthetic solution typicallycontained about 2 wt. % N-(phosphonomethyl)glycine, about 1 wt. %glycine, and about 10 wt. % sodium chloride. Other low level impuritiestypically seen in the process, such as glyphosine, NMG, HMPA, AMPA,PMIDA and phosphorous acid were also presented. The composition of thesolution is set forth in Table 4A.

TABLE 4A Components wt. % Glyphosate 1.64% NaCl 9.07% Glycine 0.89%Glyphosine 0.49% Dimethyl phosphite 0.51% H₃PO₃ 0.32% H₃PO₄ 0.40% NMG0.40% FM 0.01% FA 0.23% Na₂SO₄ 0.16% PMIDA 0.83% MAMPA 0.04% IDA 0.43%HMPA 0.43% AMPA 0.05% NFG 0.01%

The operating temperature was maintained at approximately 30° C., andthe test solution flow rate to the membrane system was maintained atapproximately 11.4 liters per minute. The operating pressure was variedfrom about 3392 kPa to about 5515 kPa. The pH of the test solution wasvaried from a pH of approx. 6.9 to a pH of approx. 10.2, by addition ofconcentrated NaOH as necessary. Feed, retentate, and permeate sampleswere collected at different pressures and pHs. HPLC results for theanalyzed samples are provided in Table 5 below.

TABLE 5 Impact of Varying Alkaline Conditions on Performance of a GEOsmonics Nanofiltration Membrane in Laboratory Evaluation System whenContacted with Test Solution Observed Permeate Flux near 3447 kPaObserved Observed (Gallons per Rejection Rejection ft² of ApproximateCharacteristic - Characteristic - membrane pH of Test GlyphosateChloride ions surface area Solution (%) (%) per day) 6.9 96.9 30.7 3.78.1 98.7 17.2 10.5 9.2 99.0 1.3 15.6 10.2 98.6 −10.1 24.0

As shown in Table 5, the pH of the test solution impacts the observedrejection characteristics and the permeate flux demonstrated by thenanofiltration membrane.

Example 6 Purification of a Test Solution with a Nanofiltration MembraneUnder Alkaline Conditions when Using Diafiltration

This example illustrates experiments conducted utilizing spiral-woundmembranes to assess the performance of a nanofiltration membrane toeffectively purify a test solution when contacting a test solution underalkaline conditions when using diafiltration.

The performance of a polyamide thin-film based nanofiltration membranewith a nominal molecular weight cut off (MWCO) of 250 daltons availablefrom GE Osmonics was evaluated as the pH of the test solution wasapproximately 9.0. The test solution flow rate was maintained atapproximately 11.4 liters per minute, the operating temperature wasmaintained at about 20° C., and the operating pressure was maintained atabout 4826 kPa.

The test solution utilized in this example is similar to the testsolution that was utilized in Example 5, except that it was combinedwith equal amounts of deionized water to simulate diafiltrationoperation. The experiment was conducted in batch-concentration mode,wherein the retentate was continually recycled to the feed vessel whilethe permeate was removed from the system and collected in a separatevessel. As noted above in connection with Example 4, prior to removal ofeach portion of permeate the system was operated in recycle mode forstabilization of the system. Feed, retentate, and permeate samples werecollected throughout the experiment as permeate was removed from theprocess. The results are reported in Table 6 below.

TABLE 6 Experimental Testing to Assess Performance of a GE OsmonicsNanofiltration Membrane to Purify a Test Solution under AcidicConditions when Using Diafiltration Permeate Removed as Permeate FluxPercentage of (Gallons per ft² Glyphosate Chloride Ions Initial Test ofmembrane Remaining in Remaining in Solution Mass surface area per TestSolution Test Solution (%) day) (%) (%) 0 28.8 100.0 100.0 12 27.6 99.387.7 23 27.6 98.4 75.1 35 25.8 97.4 62.6 46 24.0 96.2 51.0 55 22.2 94.840.3 62 20.4 93.7 33.3 70 16.8 91.7 24.0 77 13.8 89.1 16.6 84 9.6 83.78.8

As shown in Table 6, a nanofiltration membrane can be used tosufficiently remove a substantial portion of the chloride ions in a testsolution when operated in diafiltration mode under alkaline conditions.Additionally, a nanofiltration membrane can also retain a significantportion of the N-(phosphonomethyl)glycine present in a test solutionunder said conditions.

When introducing elements of the present invention or the preferredembodiments(s) thereof, the articles “a”, “an”, “the” and “said” areintended to mean that there are one or more of the elements. The terms“comprising”, “including” and “having” are intended to be inclusive andmean that there may be additional elements other than the listedelements.

In view of the above, it will be seen that the several objects of theinvention are achieved and other advantageous results attained.

As various changes could be made in the above without departing from thescope of the invention, it is intended that all matter contained in theabove description and shown in the accompanying drawings shall beinterpreted as illustrative and not in a limiting sense.

What is claimed is:
 1. A process for recovery of phosphorus values andsalt impurities from an aqueous waste stream comprising one or moreorganic phosphorus compounds and salt impurities, the processcomprising: oxidizing one or more organic phosphorus compoundscontaining phosphorus and organic carbon present in a feed streamcomprising components of the aqueous waste stream to produce aphosphate-containing cake, wherein the one or more organic phosphoruscompounds are selected from the group consisting ofN-(phosphonomethyl)glycine (glyphosate) and salts thereof,N-(phosphonomethyl)iminodiacetic acid (PMIDA) and salts thereof,aminomethylphosphonic acid and salts thereof, hydroxymethylphosphonicacid and salts thereof, N-formyl-N-(phosphonomethyl)glycine and saltsthereof, N-methyl-N-(phosphonomethyl)glycine and salts thereof, methylaminomethylphosphonic acid and salts thereof, and combinations thereof,and wherein the oxidizing one or more organic phosphorus compoundswithin the feed stream and containing phosphorus and organic carboncomprises calcination of the feed stream and/or combustion of the one ormore compounds within the feed stream and containing phosphorus andorganic carbon, wherein any combustion of the one or more compoundscontaining phosphorus and organic carbon is conducted at a temperatureof at least about 500° C.; contacting within an acidification zone thephosphate-containing cake and an acidic liquid medium to form a solutioncomprising at least one inorganic salt and phosphoric acid; andprecipitating salt crystals from the salt-containing solution to form anaqueous product mixture comprising salt crystals and a mother liquorcomprising phosphoric acid.
 2. The process of claim 1 wherein the one ormore organic phosphorus compounds are selected from the group consistingof glyphosate and salts thereof, PMIDA and salts thereof, andcombinations thereof.
 3. The process of claim 1 wherein the one or moreorganic phosphorus compounds comprise glyphosate and salts thereof. 4.The process of claim 1 wherein the one or more organic phosphoruscompounds comprise PMIDA and salts thereof.
 5. The process as set forthin claim 1 further comprising concentrating the aqueous waste steam toform at least a portion of the feed stream comprising components of theaqueous waste stream.
 6. The process as set forth in claim 5 whereinconcentrating the aqueous waste stream comprises removing water from theaqueous waste stream.
 7. The process as set forth in claim 6 whereinremoving water from the aqueous waste stream comprises heating theaqueous waste stream.
 8. The process as set forth in claim 5 whereinconcentrating the aqueous waste stream produces an overheads streamcomprising organic impurities selected from formic acid, formaldehyde,or combinations thereof removed from the aqueous waste stream.
 9. Theprocess as set forth in claim 5 wherein concentrating the aqueous wastestream comprises contacting the aqueous waste stream and a membrane toproduce a retentate enriched in organic phosphorus compounds and apermeate comprising water, and the feed stream comprises at least aportion of the retentate.
 10. The process as set forth in claim 9wherein the permeate is enriched in organic impurities selected from thegroup consisting of formic acid, formaldehyde, or a combination thereofrelative to the retentate.
 11. The process as set forth in claim 1wherein oxidizing one or more compounds containing phosphorus andorganic carbon comprises heating the feed steam by contact with anoxygen-containing gas stream.
 12. The process as set forth in claim 11wherein heating the feed stream and oxidizing organic carbon removesorganic impurities selected from the group consisting of formic acid,formaldehyde, or a combination thereof from the feed stream.
 13. Theprocess as set forth in claim 11 wherein the aqueous waste streamcomprises glyphosate or a salt thereof, the process further comprisingrecovering glyphosate from the aqueous waste stream prior to oxidizingone or more compounds containing phosphorus and organic carbon presentin the feed stream comprising components of the aqueous waste stream.14. The process as set forth in claim 13 wherein glyphosate is recoveredfrom the aqueous waste stream by evaporative crystallization, membraneseparation, and/or ion exchange.
 15. The process as set forth in claim11 wherein the aqueous waste stream is generated in a process for themanufacture of N-(phosphonomethyl)glycine or a derivative thereofcomprising oxidizing N-(phosphonomethyl)iminodiacetic acid or a saltthereof in an aqueous reaction medium in the presence of an oxidationcatalyst.
 16. The process as set forth in claim 11 wherein the aqueouswaste stream is generated in a process for the manufacture ofN-(phosphonomethyl)glycine or a derivative thereof comprising reactingglycine and dimethylphosphite.
 17. The process as set forth in claim 11wherein the aqueous waste stream comprises one or more precursors ofN-(phosphonomethyl)glycine, the process further comprising recoveringthe one or more precursors from the aqueous waste stream prior tooxidizing one or more compounds containing phosphorus and organic carbonpresent in the feed stream comprising components of the aqueous wastestream.
 18. The process as set forth in claim 17 wherein the one or moreprecursors comprise N-(phosphonomethyl)iminodiacetic acid, iminodiaceticacid, or a combination thereof.
 19. The process as set forth in claim 17wherein the one or more precursors are recovered by evaporativecrystallization, membrane separation, and/or ion exchange.
 20. Theprocess as set forth in claim 17 further comprising preparingN-(phosphonomethyl)glycine or a salt thereof.
 21. The process as setforth in claim 20 wherein N-(phosphonomethyl)iminodiacetic or a saltthereof is converted to N-(phosphonomethyl)glycine or a salt thereof.22. The process as set forth in claim 18 wherein iminodiacetic acid isutilized in a process for the preparation ofN-(phosphonomethyl)iminodiacetic acid or a salt thereof, and theN-(phosphonomethyl)iminodiacetic or a salt thereof is converted toN-(phosphonomethyl)glycine or a salt thereof.
 23. The process of claim 1wherein the oxidizing one or more organic phosphorus compoundscontaining phosphorus and organic carbon comprises calcination of thefeed stream.
 24. The process of claim 1 wherein the oxidizing one ormore organic phosphorus compounds containing phosphorus and organiccarbon comprises combustion of at least a portion of the one or morecompounds containing phosphorus and organic carbon at a combustiontemperature of at least about 500° C.